1. Field of the Invention
The present invention relates to an image forming apparatus for printing and forming an image on a printing medium the basis of an image data stored in a memory portion.
2. Description of the Related Art
An image forming apparatus forming a color image on a printing medium on the basis of a color image data is generally constructed with an image data memory portion storing an image data representative of an image to be formed on the printing medium, a image memory control portion performing writing operation control controlling writing of an image data with respect to an image data memory portion and rearing operation control controlling reading of data stored in the image data memory portion, an image processing portion performing gray scale reproduction process and color reproduction process on the basis of the data read out from the image data memory portion and thus deriving an image signal, and a printing head drive control portion generating drive control signals for respective printing head portions arranged corresponding to respective colors of printing materials, e.g. ink colors, such as cyan (C), magenta (M), yellow (Y) and black (K) and so forth, opposing to the surface of the printing medium, on the basis of the image signal from the image processing portion and supplying the drive control signals to respective printing head portions.
In the construction set forth above, when the image data supplied from an external host computer per a predetermined band width (1 band: amount to be printed on the printing medium by one time of scan of the arranged printing head), the image data is written in the image memory portion at a predetermined timing by the image memory control portion. On the other hand, the image data written in the image memory portion is read out and supplied to the image processing portion. In the image processing portion, a gray scale conversion process for respective multi-level data of color data, e.g. red (R), green (G) and blue (B) with luminance data of the image data. In conjunction therewith, binarization process utilizing gray scale or tone production method by density of each element for pseudo gray scale expression. The drive control portion generates the drive control signals for driving the printing head for performing printing operation depending upon the binarized data for the predetermined band width from the image processing portion, and supplies the drive control signals to the printing head portions. By this, when the printing head portions are scanned on the printing medium, an image is formed on the printing medium.
As forms of the foregoing input image data, there are a color data of additive color mixing type, such as data expressing R, G, B respectively and a color data of subtractive color mixing type, such as multi-value data and binary data expressing C, M, Y, K respectively. The image processing portion in the conventional image forming apparatus is fixed to one of the data types among input data expressing R, G, B, respectively or input multi-value data or binary data expressing C, M, Y, K, respectively. However, in case of coloring for a cloth, such as in screen textile printing, special ink color is used in addition to C, M, Y, K. Also, in the image forming apparatus, such as a color printer, special color for enhancing of image quality, such as high density color and low density color of the same color type printing material for enhancing tone or gray scale expression of the image, may be used. However, conventionally, since the image processing portion can be adapted to only one data type, it has not been possible to arbitrarily change the color of the printing material or to increase or decrease number of colors.